It’s entirely possible that a moderator stepped in to clear out some spam or perhaps they just nuked that entire thread you participated in... I mean, it was likely either a bit too explicit or something along those lines—there’s almost certainly a reason behind it...
Haha.... You can't actually change your username—it’s clearly stated that you should just reach out to her directly via private message and suggest the handle you want, provided it isn't a massive departure from what's already there... I mean, perhaps you could just capitalize the first letter or tack on an extra character at the end—I'm not entirely sure—but she put that specific name together with intention, so she likely knows the reasoning behind it better than anyone else. Best of luck!
You can't just post pictures whenever you feel like it—if we all did that, this entire board would be an absolute mess of clutter... which I assume is a conclusion you've already reached yourself, haha...